Two-cycle internal combustion engines are characterized by one or more cylinders consisting essentially of cylindrical bores within an engine or cylinder block. A piston fits within the cylinder such that it can move reciprocally. One end of the cylinder is closed by a cylinder head to establish a combustion chamber between a top surface of the piston and the cylinder head. The two-cycle cylinder construction differs from four-cycle cylinder construction in that the latter incorporates intake and exhaust valves in the cylinder head while the two-cycle engine has intake and exhaust ports in a wall of the cylinder.
When the piston is reciprocated to its lowest position in the cylinder, the maximum volume of the cylinder is defined. The minimum volume of the cylinder is defined when the piston is at its highest reciprocated position in the cylinder. The ratio of maximum volume to minimum volume is referred to as the compression ratio, and the greater the compression ratio, the more efficient the engine. It is believed that in most internal combustion engines, the cylinder head is manufactured with a shaped pocket or chamber, such as a dome or the like for instance, which defines the cylinder volume at the highest piston position, i.e., the aforementioned maximum volume, and therefore directly effects the performance of the engine.
It is believed that there were many past applications which required changes in cylinder head design, and such changes may have been necessitated not only by a need to vary engine compression ratio but also to adapt an engine for different octane rated fuels or for different fuels. The most common practice was to modify cylinder heads in order to develop high performance engines, and it is believed that the most common modifications to such cylinder heads was to alter the size and/or shape or the position of the combustion chamber. However, in some applications such as in racing for instance, it was often desirable to modify a cylinder head to obtain performance characteristics for the racing internal combustion engine demanded or suitable to meet immediate racing conditions. Since machining of cylinder heads to meet such immediate racing conditions was not practiced at such racing events, one of the problems presented at such racing events was the necessity of carrying and maintaining many different cylinder heads as replacement parts.
In order to overcome the aforementioned problem of carrying replacement cylinder heads, U.S. Pat. No. 4,825,817 disclosed the use of a plurality of different replaceable combustion chamber housings which could be utilized with a complementary cylinder head in order to effect different desired modifications in engine performance. However, one of the problems involved in this above discussed patented scheme is believed to be that it was necessary to carry many different ones of combustion chamber housings as replacement parts.